Mini axial fan with an improved core shaft structure

ABSTRACT

A mini axial fan includes a fan housing and a fan unit, which is mounted in the fan housing. The fan unit has a hub with integrated blades around the periphery and integrated axles at front and back sides, and two metal pins respectively press-fitted into a respective blind hole in the free end of each of the axles for rotatably supporting the fan unit on a respective bearing in the fan housing. The fan unit is injection molded from plastics and then the metal pins are installed in the fan unit so that the precision of the metal pins is maintained and the manufacturing cost of the fan unit is reduced.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a mini axial fan and, more particularly, to a mini axial fan with an improved core shaft structure for use in a computer or computer-related electronic apparatus as an effective heat dissipation device for forced air convection cooling.

(b) Description of the Prior Art

FIG. 9 shows a conventional mini axial fan for use in a computer or computer-related electronic apparatus for forced air convection cooling. According to this design, the mini axial fan comprises a fan housing 10, and a fan 20 rotatably mounted inside the fan housing 10. The fan 20 comprises a fan hub 201 and a fan shaft 202 mounted in the fan hub 201 (see FIG. 10). The fan shaft 202 is pivotally coupled to a bearing in the fan housing 10 so that the fan 20 is rotatable relative to the fan housing 10. According to the aforesaid mini axial fan design, the fan shaft 202 and the fan hub 201 are bonded together by means of insert molding, i.e., the fan shaft 202 is put in the mold of an insert molding machine by labor, and then a fluid plastic material is filled into the mold and molded into the desired fan 20. This fan fabrication method has the drawbacks of low production efficiency and low precision. Further, expansion and contraction of the plastic material during molding may cause deformation or displacement of the fan shaft, affecting the precision of the mini axial fan. Because the design trend for modern electronic products is to achieve the characteristics of being light, thin, short and small, it's difficult for the aforesaid fan fabrication method to achieve these characteristics with the expected precision. Further, the manufacturing cost of this fan fabrication method is still relatively high.

SUMMARY OF THE INVENTION

The present invention has been accomplished under the circumstances in view. It is one object of the present invention to provide a mini axial fan with an improved core shaft structure, which has metal pins respectively press-fitted into a respective plastic axle at each of two opposite sides of a plastic fan hub for rotatably supporting the fan unit inside a plastic fan housing, thereby eliminating the drawbacks of prior art insert molding technique, improving the production efficiency, and lowering the manufacturing cost.

To achieve this and other objects of the present invention, the mini axial fan comprises a fan housing and a fan unit mounted inside the fan housing. The fan housing comprises a plastic hub, which defines a backward hole, a plurality of plastic blades formed integral with and radially arranged around the periphery of the hub, two integrated plastic axles respectively extended from the front and back sides of the plastic hub at the center and axially aligned, each axle having a blind hole axially defined in the respective free end, and two metal pins respectively press-fitted into the blind holes of the axles for rotatably supporting the fan unit in the fan housing.

According to the present invention, the metal pins are respectively press-fitted into the blind holes of the plastic axles after injection molding of the plastic hub, the plastic blades and the plastic axles, and therefore the installation precision of the metal pins is free from the expansion and contraction effects of the plastic material during the injection molding of the fan unit, i.e., the invention eliminates the drawbacks of the aforesaid prior art mini axial fan design that employs an insert molding technique.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded view of a mini axial fan in accordance with the present invention.

FIG. 2 is an assembly view of the mini axial fan shown in FIG. 1.

FIG. 3 is a sectional view of the mini axial fan in accordance with the present invention.

FIG. 4 is a schematic sectional view of a part of the present invention, showing the conical point of the pin positioned in the recessed hole of the associated bearing.

FIG. 5 is an oblique top view of the fan unit of the mini axial fan according to the present invention.

FIG. 6 is an oblique bottom view of the fan unit of the mini axial fan according to the present invention.

FIG. 7 is an exploded sectional view of the fan unit of the mini axial fan according to the present invention.

FIG. 8 is a sectional assembly view of FIG. 7.

FIG. 9 is an oblique top view of a mini axial fan according to the prior art.

FIG. 10 is a sectional view of the fan unit of the mini axial fan shown in FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in the annexed drawings in detail, a mini axial fan comprises a fan housing 1 and a fan unit 2 mounted in the fan housing 1.

As shown in FIGS. 13, the fan housing 1 is a plastic frame shell having a motor stator 11 mounted therein for driving the fan unit 2. The fan housing 1 can be made in a rectangular shape as shown in the annexed drawings, in or any other geometric shape. The fan housing 1 comprises a circular fan accommodation chamber 12, two bearing holders 13 disposed at top and bottom sides in the circular fan accommodation chamber 12, a plurality of radial ribs 14 respectively equiangularly spaced around the bearing holders 13 and respectively connected between the bearing holders 13 and the peripheral wall of the fan housing 1, and two bearings 15 formed of a metal or ceramic material and respectively mounted in the bearing holders 13 at an inner side. Each bearing 15 has a recessed hole 151 at the center for the positioning of a respective pin 27 of the fan unit 2. The aforesaid motor stator 11 is an electric device mounted in between the bearing holders 13 for driving the fan unit 2.

Referring to FIGS. 5˜8, the fan unit 2 comprises a hub 21, which defines a backward hole 23, a plurality of blades 22 radially arranged around the hub 21, a motor rotor 24 mounted in the backward hole 23 inside the hub 21, two axles 25 and 25′ respectively extending from the front and back sides of the hub 21 at the center and axially aligned and having a respective blind hole 26 axially defined in the respective free end, and two pins 27 respectively press-fitted into the blind holes 26 of the axles 25 and 25′ and terminating in a respective conical point 271 outside the axles 25 and 25′ (see FIGS. 7 and 8). The blades 22 can be configured to provide 3D curves, or made in any of a variety of other shapes. The hub 21, the blades 22 and the axles 25 and 25′ are injection-molded from plastics in one piece. Further, the pins 27 are formed of high carbon steel or zirconium, having the characteristics of high hardness and excellent wear-resistance suitable for a prolonged service life of the fan.

Thus, as shown in FIGS. 1 and 2, the fan unit 2 is mounted in the circular fan accommodation chamber 12 of the fan housing 1 to receive the motor stator 11 in the backward hole 23 of the hub 21, i.e. the motor stator 11 and the motor rotor 24 are matched to each other. At the same time, the conical points 271 of the pins 27 are respectively positioned in the recessed holes 151 of the bearings 15 (as shown in FIG. 4). When the mini axial fan is assembled (as shown in FIG. 2), it can be used in a computer or computer-related electronic apparatus as an effective heat dissipation device for forced air convection cooling.

During the fabrication of the core shaft structure of the mini axial fan, the hub 21, the blades 22 and the axles 25 and 25′ are injection-molded from plastics in one piece, and then the pins 27 are respectively press-fitted into the blind holes 26 of the axles 25 and 25′ by means of a tool (see FIG. 7), leaving the conical points 271 of the pins 27 protruded outside the axles 25 and 25′ (see FIG. 8). This design simplifies the fabrication of the fan 2, facilitating molding and mold stripping operations. Therefore, the invention is suitable for mass production to lower the manufacturing cost. After injection molding of the hub 21, the blades 22 and the axles 25 and 25′, the pins 27 are accurately fastened to the blind holes 26 of the axles 25 and 25′ by means of a machine or tool, thus eliminating the drawbacks of the conventional insert molding technique in which the shaft is embedded in the mold before molding and the expansion and contraction of the plastic material would cause the shaft to deform. Therefore, the fan unit 2 of the present invention meets the requirements of a mini axial fan having the characteristics of small size and high precision. Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims. 

1. A mini axial fan, comprising a fan housing and a fan unit mounted in said fan housing, wherein said fan unit comprises: a hub, said hub defining a backward hole; a plurality of blades formed integral with and radially arranged around the periphery of said hub; two axles respectively extending through the center of a front side and through the center of a back side of said hub and axially aligned with each other, each said axle having a free end and a blind hole axially defined in the free end; and two pins respectively press-fitted into the blind holes of said axles for rotatably supporting said fan unit in said fan housing.
 2. The mini axial fan as claimed in claim 1, wherein said fan housing is a rectangular plastic frame shell, comprising a circular fan accommodation chamber, and two bearings respectively disposed at top and bottom sides of said circular fan accommodation chamber and facing each other, each said bearing having a recessed hole at the center thereof; and said fan unit is mounted in said circular fan accommodation chamber between said bearings, having said pins positioned in the recessed holes of said bearings.
 3. The mini axial fan as claimed in claim 2, wherein said fan housing further comprises two bearing holders respectively disposed at top and bottom sides of said circular fan accommodation chamber to support said bearings in place, a plurality of radial ribs respectively equiangularly spaced around said bearing holders and respectively connected between said bearing holders and the periphery of said fan housing, and a motor stator affixed to one said bearing holder; and said fan unit further comprises a motor rotor mounted inside said fan hub.
 4. The mini axial fan as claimed in claim 2, wherein each said pin has an outer end terminating in a conical point outside the respective axle and positioned in the recessed hole of a respective one of said bearings.
 5. The mini axial fan as claimed in claim 1, wherein said pins are made of a high carbon steel.
 6. The mini axial fan as claimed in claim 1, wherein said pins are made of zirconium. 